Telephone system



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March 27, 1945. H. M. BAscoM ETAL TELEPHONE SYSTEM 17 Sheets-Sheet 17 Filed March 4, 1942 HMaAsoM VvE/v Tons u. c. 6000A no A T TOR/VE Y Patented Mar. 27, 1945 ".'vii

UNITED STATES PATENT OFFICE TELEPHONE SYSTEM Application March 4, 1942, Serial No. 433,348

14 Claims.

This invention relates to telephone systems and particularly to systems employing impulse controlled switches for completing connections between calling and called subscribers' stations.

Objects of the invention are the improvement and simplification of systems comprising an automatic oce adjacent a metropolitan area, .the provision of eicient and reliable means in such an oflice for discriminating between local calls, calls completed over direct interoiiice trunks, and calls completed through a tandem oiiice in the metropolitan area, and the provision of means for local and extended service in such an omce with further provision for variable charging rates.

Where an automatic telephone oice isadjacent a large metropolitan area served by a plurality of telephone oilices, calls originating in the oilice may be local calls, calls to subscribers in adjacent exchanges to which direct, trunks are available, c-r calls to subscribers in offices in the metropolitan area, the last-mentioned calls being routed through a tandem oice in the metropolitan area. The number of digits in the directory listed numbers of subscribers in the local, adjacent, and metropolitan oices may vary; and provision must be made for both local and extended area message rate service and for overtime and zone registration.

Applicants invention is a new, improved and eicient trunking arrangement and equipment for use in an automatic telephone oiice having having local and extended area message rate subscribers, this oiilce being adjacent a metropolitan area including a tandem oice through which calls to subscribers in the metropolitan area may be routed. According to this invention, a calling line in an automatic telephone oiiice is automatically connected by a rst group selector switch to an idle translating trunk` circuit'which is arranged to register the called office code and be restored to normal to effect release of the'rst group selector on local calls to enable operation of this selector responsive to the first digit following the office code, a part or all f the called oice code being registered by a two-motion group selector switch which is restoredto normal after the office code has been dialed on all calls except callsy to zero operator and which is reoperated on calls other than local calls to select a. group of direct interoiilce trunks ora group of trunks to a tandem ofce according to the called oilice code, the oce code and numerical digits being transmitted over a selected interoice or tandem trunk and the numerical digits alone being transmitted over certain of the direct interoiiice trunks` A feature of the invention is a translating trunk circuit of the above-described character which is adapted to receive both two and threedigit oice codes, an auxiliary selector being provided for registering the lastl two digits of threedigit ofllce codes.

Other features of the invention are the provision of means in a translating trunk of the above-described character for indicating the class of service to which the calling station is entitled on calls to an operator and the provision of means for controlling the operation of a calling subscribers messagamgsion calls requiring more than one operation of the register.

These and other features of the invention will be better understood by considering a system in which the invention is embodied, one such system being shown schematically in the drawing which forms a part of this specification. The invention is not limited in its application to the system represented in the drawings, but is generally applicable to systems comprising a local automatic ofce adajacent a metropolitan area.

Referring to the drawings:

Fig. 1 shows a subscribers station A and line LI, a connector switch CI and part of a line nder LFI;

Fig. 2 shows the remainder of the line finder LFI;

Fig. 3 shows a line-iinder control circuit and allotter switch;

Fig. 4 shows a message register trunk circuit MRT associated with the line finder LFI of Fig. 2;

Fig. 5 shows a first selector SI associated with the trunk circuit MRT of Fig. 4;

Figs. 6 to 14, inclusive, show a translating trunk circuit 'I'I comprising a group selector TTS, an auxiliary selector AS, a multiregistration control switch MRS, and a sender selector SS;

Figs. 15 and 16 show a register sender;

Fig. 17 shows the trunking plan of a system comprising the circuits shown in Figs. 1 to 15, inclusive; and

Fig. 18 shows the relative position in which Figs. 1 to 16 are to be placed to form an operative arrangement.

GENERAL DESCRIPTION Referring iirst to the system and trunking arrangement shown in Fig. 17, subscribers lines terminate in the banks of line-finder switches. There may be separate groups of line nders for the lines of subscribers restricted to local service and the lines of subscribers entitled to extended area service. The station A represents a group which is entitled to extended area service and the station B represents a group which is only entitled to local service. A single group of line finders may, however, serve both restricted and extended service subscribers. The line nder LFa represents a group which serves lines including message rate lines, the line nder LFa being connected by a message rate trunk circuit MRT to a rst selector SIa. The line iinder LFb represents a group which serves at rate lines entitled only to local service, the line nder LFb being connected directly to a first selector SIb The selectors SIa and SIb have access to connector switches for completing local calls and have access on the rst level to discriminating or translating trunk circuits 'ITa and TTb respectively. Upon connection of a calling line to a rst selector, the selector is automatically operated to hunt for an idle discriminating trunk circuit 'IIa or 'I'l'b as the case may be. The trunk circuit TTa includes a trunk selector TSa and the trunk circuit TTb includes a trunk selector TSb, which selectors have access in common on the tenth level to trunks to zero operator, on level I to trunks to toll operator, and on level 4 to trunks to information operator. The selector TSa also has access on the second level to trunks to a crossbar tandem office in an adjacent metropolitan area and on the third, fifth and sixth levels to trunks to other step-by-step ofces. The trunk circuit TTa includes a switch SS for selecting an idle register sender RS for use on calls other than local calls or calls to an operator. If desired, each translating trunk circuit may be provided with an individual register sender. The trunk circuit TTb does not include a register sender or have access to a group of such senders since the associated lines are not entitled to extended service. Each of the trunk circuits TTa and 'I'Tb are arranged to respond to the oice code digits dialed by a connected calling subscriber, the associated trunk selector responding to the rst digit dialed. If the rst digit is 0, the brushes of the selector are selectively stepped up to the tenth level and automatically advanced to nd an idle trunk to an operators position. While not shown in Fig. 17 an auxiliary switch may be provided in each of the trunk circuits Tra and TTb in case the code of any called cnice includes more than two digits.

In any event, two digit codes are registered by selective vertical and rotary movement of selectors TSa and TSb. I

If the called ofl'lce code, as registered in a discriminating trunk circuit 'I'Ta or 'ITb is the local oice code, the discriminating trunk circuit is restored to normal; and the first selector, by which the discriminating trunk circuit was selected, is also restored to normal so as to be ready for operation in response to the first digit dialed after the oiiice code. While the bank of selectors SIa and SIb are shown as connecting directly to connector switches, intermediate selectors may be provided if the number of lines in the local ofllce requires an additional stage of selection. The desired connection is completed by the operation of a connector under the control of the calling subscribers dial in f'the usual manner. If the calling subscriber connected to a trunk circuit TTa or are provided with a fourth conductor through which a class of service signal is transmitted to the answering operator. If the calling subscriber dials the code of an adjacent local oillce to which direct trunks are available in the banks of selectors TSa, the selector TSa is restored to normal and reoperated automatically to select the proper level and an idle trunk therein. The third, fth and sixth levels of selectors TSa are represented in Fig. 17 as being levels in which the terminals are connected to direct interoflice trunks.

If the calling subscriber dials the code of an office which is reached through the metropolitan tandem oice, the trunk selector TSa is restored to normal and automatically reoperated to select an idle trunk in the level in which the terminals are connected to trunks to the tandem oilice. The sender selector SS of the discriminating trunk circuit 'ITa is a preselector which is advanced to an idle register sender RS wherever the register sender to which the trunk circuit is then connected becomes busy; and all digits of the called subscribers number are registered in the selected register sender on calls, other than local calls and calls to an operator. If the call is routed over a direct trunk, the oii'ice code digit may or may not be transmitted, in addition to numerical digits, by the register sender to the called oice. On a call routed through the tandemoiice, the register sender transmits both the oflice code and the numerical code over the selected trunk.

The subscribers stations A, B and X are of the usual type provided in common battery.` automatic oinces, each station being provided with a dial or other impulse sending device for controlling the establishment of desired connections. The line finder, selector and connector switches are of the two-motion step-by-step type. Reference may be had to "Automatic Telephony by Smith and Campbell, 2nd edition, pages 53 to 65, inclusive, for a description of the structure of such switches and their operation as selectors and connectors. Reference may be had to the patent to T. L. Dimond 2,210,068, August 6, 1940, for a detailed description of a two-motion line nder and and associated line-lnder control and allotter circuit.

The circuits shown in Figs. 1 to 16, inclusive, conform to the trunking plan shownin Fig. 17 except that the tandem trunks which are connected to the, last five sets of terminals in the second level of the bank of selectors TTS are also connected to corresponding sets of terminals in the third, fth and sixth levels. The operation of the system represented in Figs. 1 to 16, inclusive, will be described for various types of call. g

DETAILED DESCRIPTION Connection of calling line to translating trunk circuit Assuming that a call is initiated atV station A, a circuit is closed for operating relay -zl II of line circuit LCI, this circuit being traced from battery through the middle and right windings and inner right back contact of relay III, loweri conductor of line LI, through the telephone and dial at station A, back over the other conductor of line LI, through the left back contact and left winding of relay III to ground. Relay III is partially actuated to close its front contacts without opening its back contacts, thereby connecting the middle winding of relay I I I to conductor I IB, connecting ground through conductor II2 to a terminal of commutator |31 to identify the level of the banks of the line finders in which is located the set of terminals to which the line LI is connected, and connecting ground through resistor I2I, conductor |20, and a front contact of the normally operated transfer relay 351 of the line-finder control circuit LFC to the winding of start relay 350. Relay 350 operates, closing a circuit for operating relay 35 I, this circuit being traced from battery through the winding of relay 35|, inner lower back contact of relay 354, a lower back contact of relay 353, front contact, of relay 350, to ground. Assume that the brushes of the allotter switch are in engagement with the terminals to which the line finder LFI is connected and that this finder is idle at the time relay 350 operates. Relay 35| locks through its outer lower front contact, under the control of relay 354 and closes `a. circuit for operating line relay 50| of selector SI and relay 39| of the line-finder allotter circuit LFC. The circuit for operating relays 53| and 39| is traced from battery through the upper winding of relay 50|, inner lower back contact of relay 504, conductor 4I2 of trunk circuit MRT, lower back contact of relay 401, lower winding of relay 400, conductor 202, conductor 292, terminal and brush of bank 315 of the line-nder allotter LFC, a lower back contact of relay 354, inner lower front contact of relay 35|, winding of relay 39|, to ground at a back contact cf relay 393. Relay 50| closes a circuit for operating slow-to-release relay 502; and relay 532 connects ground to conductor 4I3 of trunk circuit MRT to hold the line-nder circuit LFI after it has established connection with the calling line as hereinafter described. The operation of relay 39| closes a circuit for operating relay 392 and prevents the operation of the vertical stepping magnet 243 of the allotted line nder LFI until the selector SI has been operated to select the terminals of a translating trunk in the rst level of its bank, as hereinafter described. Relay 392 closes a circuit for operating relay 303 and connects ground to the winding of relay 39| to maintain the operation of relay 39| after relay 333 has operated. Relay 393 closes a circuit for operating relay 394. Relay 394 locks through its lower front contact under control of relay 35|; and causes the release of relay 392, thereby opening the circuit through the winding of relay 39| and the upper winding of relay 50| to cause the release of these relays. The release of relay 39| causes the release of relay 392; the release of relay 392 causes the release of relay 393; and relay 393 reconnects ground to the winding of relay 39| to effect the reoperation of relays 39| and 50|. Relay 393 is slow in releasing to insure the release of relays 39| and 50|. Thus the operation and release of relays 392 and 393 is eiective to simulate the transmission of one dial pulse to the line relay 50| to operate selector SI, as hereinafter described. The aforementioned operation of relay 35| of allotter circuit LFC also closes a circuit for operating the stepping -relay 352, this circuit being traced from battery through the lower winding of relay 352, inner upper front contact of relay 35|, brush and termina] of bank 314 of the allotter switch, conductor 285, back contact of the eleventh rotary step springs 246. upper back contacts of relays 242 and 24|, through the back contacts of vertical stepping magnet 243 and rotary stepping magnet 244 of the line nder LFI, to ground. The operation of relay 352 closes a circuit from ground at the inner upper back contact of relay 354, through the front contact of relay 352, upper- Iii',

most back contact of relay 353, through the upper back contact of relay 39| or through the upper front contact of relay 394, brush and terminal of bank 313 of the allotter switch, conductor 293, to the winding of the vertical stepping magnet 243 of line finder LFI. Magnet 243 operates, stepping the two sets of brushes of line finder LFI up to the rst level of the terminal bank. The vertical off-normal springs 245 are` actuated when the shaft on which the brushes are mounted moves out of normal position. The operation of magnet 243 opens the operating circuit of relay 352; but, if the calling line is connected to terminals in the first level of the lineflnder bank, relay 352 is held operated to prevent the reoperation of magnet 243. The circuit forliolding relay 352 operated is traced from battery through the lowenwinding of relay 352, inner and middle upper front contacts of relay 35|, upper winding and inner upper back contact of relay 353, uppermost back contact of relay 354, brush and terminal of bank 312 of the allotter switch, conductor |39, commutator brush |38 and first segment of commutator |31 of line finder LFI, through conductor II2 to ground at the right front contact of relay III. Relay 353 is partially operated by the energization of its upper winding in this circuit so as to close its lowermost contact and thereby operatively energize its lower locking winding under control of relay 35|. The complete operation of relay 353, due to the energization of its locking winding, opens the circuit through its upper winding, opens the operating circuit of stepping magnet 243 and closes a circuit for operating the rotary stepping magnet 244. Relay 353 is slow in operating so that the brushes of the line finder will stop vibrating before the circuit is closed for operating the rotary stepping magnet. The circuit for operating the rotary stepping magnet 244 is traced from battery through its winding, conductor 294, terminal and brush of bank 316 of the allotter switch, uppermost front contact of relay 353, front contact of relay 352, to ground at a back contact of relay 354. The operation of magnet 244 steps the brushes of the line-nder switch into engagement with the rst set of terminals in the level to which the brushes were advanced by the operation of magnet 243. The operation of the magnet 244 opens the circuit through the lower winding of relay 352; and relay 352 releases unless a calling line is connected to the terminals engaged by one of the sets of brushes of the line finder. If neither of the two lines connected to the terminals engaged by the brushes is a calling line awaiting connection to a first selector, relay 352 releases when the circuit through its lower winding is opened by the operation of magnet 244. The release of relay 352 causes the release of stepping magnet 244; and the release of stepping magnet 244 again closes the operating circuit for relay 352. Relay 352 and stepping magnet 244 are thus alternately operated and released to advance the brushes of the line iinder. step by step. until the one or the other of the two sets of brushes engages the terminals of the calling line; whereupon relay 352 .is held operated and one or the other of relays 24! and 242 are operated. Assuming the calling line LI to be found by the upper set of brushes, a circuit is closed for holding the stepping relay 352 operated and for operating relay 24|. This circuit is traced from ground through the upper winding of relay 352, inner upper front contact of relay 353, uppermost back contact of relay 

